Hydraulic jar device

ABSTRACT

An arrangement by a hydraulic jar device, especially for use in underground wells, where the jar device is installed in a pipe string led down into the well, and designed so that e.g. a stuck object in the well may be loosened or broken up by upward or downward percussions from the jar device. The jar device is actuated by increasing the flow of drill fluid. Alternatively, the device is actuated by compression. A valve ( 27, 37, 38 ) closes off the flow of drill fluid, whereby a percussion cycle is initiated. The valve is designed so as also to seal during strong lateral accelerations.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage of International Application No.PCT/NO01/00513, filed Dec. 28, 2001 and published under PCT Article21(2) in English, and claims priority of Norway Application No.20010059, filed on Jan. 5, 2001. The aforementioned related patentapplication is herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention regards an arrangement by a hydraulic jar device,especially for use in underground wells, where the jar device isinstalled in a pipe string led down into the well, and designed so thate.g. a stuck object in the well may be loosened or broken up by upwardor downward percussions from the jar device, where the jar devicecomprises a casing member, a connector sleeve, a jar, the casing memberand connector sleeve each having separate longitudinal through bores,while the jar has a bore such that hydraulic liquid may pass in the jardevice, and where the jar device is provided with a piston associatedwith a valve designed to close and open a bore during the percussioncycle, the piston valve being designed, respectively, to be closed bythe inflow of hydraulic liquid and be opened by a tension springtensioned during the percussion cycle, when the spring force of thetension spring exceeds the pressure from the inflowing hydraulic liquid,to enable the piston to displace the jar relative to the casing memberin order to carry out the percussion.

2. Background of the Related Art

Such jar devices are often used in connection with anchoring of valves,measurement equipment and other equipment downhole. The jar device isprovided in a pipe string, e.g. a drill pipe string or coiled tubing,and equipment to be placed in the well is fitted to the lower end of thejar device. As mentioned, the jar device is provided with a passage suchthat inflowing liquid may pass before the jar device is actuated forpercussion. The equipment to be placed in the well may be equipped withgrippers, spring bosses or something else that will grip e.g. grooves orseating areas in the wall of the well. In order to ensure that theequipment does not come loose, it is often provided with a lockingdevice to be actuated when at least one shear pin is broken off. Inthose cases where the pipe string is not able to transfer sufficientforce to break off at least one shear pin, it may be broken by means ofthe jar device. Moreover, the jar device is often used purely as ameasure, so that the equipment may be loosened, were it to get stuck.

Such hydraulic jar devices are often pre-tensioned by means of anexternal spring over the jar device. Alternatively, a long drill stringor coiled tubing may constitute the spring element. The percussion iscarried out by impact areas on the jar device being moved apart,whereupon the pre-tensioned spring sends the impact areas back towardseach other. As mentioned, the jar device comprises a hydraulic pistonprovided with a passage and an associated valve. The valve is normallyopen, so that liquid may pass through the piston of the jar device whennot actuated for percussion. When the jar device is to be actuated forpercussion, increasing the flow rate of the inflowing hydraulic liquidcloses the passage, so that the valve is closed at the time in questionduring the percussion cycle. Alternatively, pushing the jar into thecasing member may in one embodiment actuate the device. At this, thepiston and also the impact areas of the jar device will be displacedrelative to each other during the preparation for the percussion. At thesame time, the spring is tensioned further as a result of the movementin the jar device. The piston valve is opened when, during thepercussion cycle, the jar device has been brought to the extremeposition in question, to allow the liquid to flow through the pistonagain. The hydraulic force against the piston will then suddenlydecrease, and the external, associated spring over the jar device willsend the impact areas against each other in order to carry out thepercussion, whereupon the percussion cycle is repeated.

The use of a spring that can be pre-tensioned from the outside in orderto drive the percussion in the jar device is known. It is further knownto design the spring so as to allow it to be pre-tensioned either bypulling the pipe string in the direction away from the jar device orpushing the pipe string in the direction towards the jar device. Themagnitude of the impact force may be varied through the pre-tensioningof the spring. When the pre-tensioned spring over the jar device is in aneutral position, hydraulic liquid may be passed through the pipe stringwithout actuating the jar device. The jar device is actuated forpercussive movement by a pressure increase in the hydraulic liquidcontained in the jar device; this will result in cyclic closing andopening of the piston valve, so that the jar device prepares andperforms the percussion in the percussion cycle by displacing therelevant components of the jar device, whereupon the procedure isrepeated for new percussions. In one embodiment, the jar device may, asmentioned above, be actuated through the jar being pushed into thecasing member.

In many of the known jar devices, see e.g. U.S. Pat. Nos. 4,807,709,3,570,611, 3,379,261 and 3,361,220, the weight of the equipment hangingfrom the jar device is often sufficient to actuate the piston valve, soas to close the passage for the hydraulic liquid, thereby actuating thepercussion effect. This means that it is not possible to circulateliquid through the pipe string when the jar device is being run into orout of the well. If prolonged circulation is required, the percussioneffect may damage the equipment. The hydraulic parts of the jar devicesuch as the piston and valve components, will become worn duringoperation and therefore require regular replacement. Upon lengthyoperation requiring circulation of liquid, parts of the jar device maywear significantly before the jar device comes to be used in therequired operations. This may result in a reduced percussion effect andfaulty operation. However these are conditions that have essentiallybeen remedied by the jar device according to NO patent 304 199. Here, anefficient, reliable and robust hydraulic jar device of theabove-mentioned type has been provided through relatively simple andreasonable means. Furthermore, circulation of liquid such as drill fluidthrough the jar device is possible without this being actuated uponpre-tensioning of the spring, and it is possible to initiate thepercussion effect by increasing the pressure of the inflowing volume ofliquid, as the piston valve can not close until there is an increase inpressure in the inflowing liquid.

However the known jar devices, especially jar devices with upwardpercussions, suffer from a shortcoming in that the impact areas inquestion are provided on the outside of the jar device. Consequently,the percussion effect may be limited by influences from the outside ofthe jar device, e.g. by contaminants depositing between the impactareas. Another shortcoming of known jar devices is that the hydraulicliquid can close the piston valve before the impact areas has reachedfull impact against each other during the final period of the percussioncycle. This means that the liquid over such a prematurely closed pistonvalve will brake the percussion and give a reduced percussion effect.

SUMMARY OF THE INVENTION

In consequence, one object of the invention is to provide a jar deviceof the above-mentioned type, where these shortcomings of previous jardevices have been remedied. Another object is to provide a jar device ofthe simplest and most reliable construction possible. These and anyother objects have been realised in the manner that appears from thecharacterising part of the present independent claim. In accordance withthe invention, a piston valve is constructed in a manner such that thesealing body of the valve, which in a preferred embodiment is a ball, isguided via a precise valve guide towards a valve seat where the valvebody is supported radially by the valve guide, also in the closedposition. The valve is thereby safeguarded against inadvertent opening,e.g. upon the jar device being subjected to great lateral acceleration.A bore in the piston is kept open with clear passage for the hydraulicliquid through the piston, at least until the percussion that during thepercussion cycle is triggered by the valve opening, has been completed.Thus the percussion will not be braked by trapped hydraulic liquid andas a result give a reduced percussion effect. Other beneficial featuresof the invention appear from the claims and the rest of thespecification.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, which exists in two embodiments of which one describes anupward striking jar device and one describes a downward striking jardevice, will in the following be explained in greater detail withreference to the drawings, in which:

FIG. 1 is a longitudinal section of the present upward striking jardevice, comprising a casing member, a lower connector sleeve and a jar,where the lower end of the jar is equipped with a movable pistonprovided in a longitudinal through bore in the casing member, and whichis associated with a valve in the form of a valve ball, an intermediateseating area and a lower valve body, where the jar device is in anon-actuatable position with clear passage for hydraulic liquid throughthe casing member, the jar and the connector sleeve;

FIG. 2 is a longitudinal section of the midsection of the jar device, ona larger scale, where the impact collar has been brought to a stopagainst the end socket. In this position, the jar device is ready tocommence a percussion cycle, but still has a clear passage for hydraulicliquid through the casing member, the jar and the connector sleeve;

FIG. 3 shows the same longitudinal section, where the valve body isdisplaced as a result of an increased volumetric flow of liquid, so thatthe ball closes against the seating area. The liquid pressure againstthe piston and the ball displaces the piston downwards while the pistontensions a lower tension spring by means of the valve body;

FIG. 4 shows the same longitudinal section, where the piston and thevalve body are displaced fully in the tensioning direction as a resultof the liquid pressure, so that the valve body abuts the connectorsleeve. The liquid pressure against the ball tensions the tension springby means of the valve body;

FIG. 5 shows the same longitudinal section, but here the valve ball hasbeen lifted off the seating area to allow liquid to flow through thepiston, whereby the jar is free to be displaced in the direction ofpercussion;

FIG. 6 shows various sections through the jar device at lines A—A, B—Bin FIG. 2;

FIGS. 7 a–b show a longitudinal section of the present downward strikingjar device, comprising a casing member, a jar and a connector piece,where the casing member comprises a longitudinal through bore equippedwith a movable piston provided in a through piston bore, and which isassociated with a valve in the form of a seating area, an upper valveball and a lower valve body over and under the seating area,respectively, where the jar device is in a non-actuated position withclear passage for hydraulic liquid through the casing member, the jarand the connector sleeve;

FIGS. 8 a–b show the same longitudinal sections as FIGS. 7 a–b, but herethe jar device is compressed further, and the piston is moved to aposition in the percussion cycle in which the ball is brought intosealing contact against the collar of the piston. Compressed oil isflowing to the upper side of the piston, initiating the downward pistonmovement;

FIGS. 9 a–b show the same longitudinal section as FIGS. 7 a–b, but herethe piston and valve body have been moved to a lower extreme positionduring the percussion cycle, while a tension spring associated with thevalve body is tensioned, making the jar device ready for a percussion;

FIGS. 10 a–b show the same longitudinal section as FIGS. 7 a–b, but herethe percussion has been triggered by the valve body having lifted thevalve ball off the seating area as the spring tension in the associatedtension spring tensioned during the percussion cycle exceeds thepressure from the inflowing hydraulic liquid; and

FIGS. 11 a–c show various sections through the jar device at is thecutting lines A—A, B—B and C—C in FIGS. 8 a–b.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

First of all, an embodiment is described with reference to FIGS. 1 to 6,in which the jar device is designed to strike upwards.

The present jar device designed to strike upwards comprises a tubularcasing member 1 having a longitudinal through bore 2 so as to allowpassage of hydraulic liquid through the casing member 1. The lower endof the casing member 1 is connected to a connector sleeve 3 with alongitudinal through bore 4 for passage of hydraulic liquid. Theconnection between the casing member 1 and the connector sleeve 3 mayfor instance be constituted by a threaded connection 5 formed internallyof the casing member bore 2, and which is made pressure tight in anappropriate manner. With this, the lower end of the jar device may becoupled to the tool, pipe string etc. (not shown) in question by meansof e.g. a lower male threaded connection 6 on the connector sleeve 3.

The upper end of the casing member 1 is such that a jar 7 may bedisplaced upwards relative to the casing member 1 when the jar device isactuated for percussion effect by an increase in the rate of flow of theinflowing hydraulic liquid. In order to facilitate the axialdisplacement of the jar 7, the casing member 1 is provided with anaxially split end socket 8. The casing member 1 and the end socket 8 arefixed to each other by means of e.g. a threaded connection 9 that islocated internally of the upper end of the casing member bore 2, andwhich is pressure tight. Further, a lower section 10 of the jar 7 isduring the percussion cycle movably guided into a longitudinal throughbore in the end socket 8. The lower jar section 10 is in slidingabutment against an upper end socket section 11 made pressure tight byan appropriate seal 12 and a lower end socket section 13 made pressuretight by e.g. a compression packing 14, respectively. Furthermore, aseal 15 has been provided to seal against pressure between the casingmember bore 2 and the lower end socket section 13.

In addition, the jar 7 has an upper bore 16 provided with a femalethreaded connection 17, so as to allow the jar device to be coupled to adrill string, coiled tubing etc. (not shown) in a pressure tight manner.The upper jar bore 16 changes into a longitudinal bore 18 that ends upin a vertical gateway 19 at a distance above the lower section 10 of thejar, so that hydraulic liquid may pass through the jar 7 and further outinto the casing member bore 2, as shown in FIG. 1.

Furthermore, the jar 7 includes an external, projecting flange-likeimpact collar 20. With this, the lower, wider section of the impactcollar 20 forms an upward facing impact area 21 designed to impactagainst a downward facing impact area 22 in a midsection of the endsocket 8 on the casing member 1. The upward facing impact area 21 on theimpact collar 20 is located in an annulus 23 formed by a recess in theend socket 8 between the downward facing end socket impact area 22 andthe lower end socket section 13, respectively. The impact collar 20further has dimensions that allow the lower, wider section of the impactcollar 20 to abut the inner wall of the annulus 23 in a sliding manner.As is apparent from FIG. 1, the impact areas 21, 22 on the jar 7 and theend socket 8 are spaced apart when the jar device is in an inactivestate.

The impact collar 20 is further provided with at least one verticalpassage 24 that extends from the underside of the impact collar 20 andup to an associated passage 25 in the upper section 11 of the endsocket. The passage 25 ends in a gateway 26. This means that thehydraulic liquid in the annulus 23 between the lower section 10 of thejar and the end socket 8 has an outlet from the jar device via this atleast one passage 24 in the impact collar 20, together with passage 25and gateway 26 in the end socket 8.

In addition, the jar device comprises a piston 27 that, among otherthings, makes it possible to move the jar 7 when the jar device has beenactuated by an increase in the liquid flow of inflowing hydraulicliquid. The piston 27 is fixed to the lower end of the jar 7 underneaththe gateway 19 by the end of the jar bore 18, and this fixing isachieved by e.g. a threaded connection 28. A lower section 29 of thepiston 27 is in sliding abutment against the inner wall of the casingmember bore 2 during the percussion cycle, and is pressure sealed bye.g. an upper compression packing 30 and a lower, relatively wide seal31. An upper section of the piston 27 has cross section that is a littlesmaller than that of the casing member bore 2, so as to allow theformation of an annulus 32 on the outside of and above the upper pistonsection 27 for the passage of hydraulic liquid. At least one gateway 33leads from the piston annulus 32 and into a lower bore 34 positionedcentrally in the lower section 29 of the piston. The piston bore 34 hasan upper section, the valve guide 34′, the diameter of which is slightlylarger than that of the midsection of the piston bore 34, and themidsection becomes a lower section that slopes out towards a lowerpiston area 35. The piston has an upper piston area 36, and the upperend of the lower piston section 29 will likewise form an intermediatepiston area.

The passage for hydraulic liquid through the piston bore 34 may be shutoff by a valve consisting of a (valve) ball 37, an intermediate seatingarea 38 and a lower valve body 39. The ball 37 is located in an uppersection of the piston bore 34, and has approximately the same diameteras the valve guide 34′. The seating area 38 is formed in the transitionzone between the upper section and midsection of the piston bore 34. Theseating area 38 further has a form that causes the ball 37 to sealagainst it during the relevant periods of the percussion cycle. Thevalve body 39 has an upper section that runs into the piston bore 34 anda lower section that runs on the outside of the piston 27, down towardsan upper end face 40 of the connector sleeve 3. An upper seating area onthe valve body 39 will normally abut the lower side of the valve ball37. Otherwise, the lower section of the valve body 39 has a crosssection that is slightly larger than that of the upper section. Thetransition zone between these sections of the valve body 39 slopes in asimilar manner to the lower section of the piston bore 34, and isprovided with upward facing fins 41. The fins 41 on the valve body abutthe lower, outward sloping section of the piston bore 34, partly whenthe jar device is not in the actuated state and partly when thepercussion has been triggered following opening of the valve 37, 38, 39in the piston bore 34, as can be seen from FIGS. 1, 2 and 5.

The valve body 39 is equipped with a sliding valve 42 that is movable ina recess 43 at the bottom end of the valve body 39, as shown in FIGS. 1and 2. Furthermore, the sliding valve 42 is associated with a lowertension spring 46 that is tensioned during the percussion cycle whenpreparing for the impact between the impact area 21 of impact collar 20and the impact area 22 of the jar 7, respectively. As can be seen fromFIG. 3, the tensioning of the lower tension spring 46 takes place viathe valve body 39 when the piston 27 is displaced downwards in thecasing member bore 2 during the relevant period of the percussion cycle.Otherwise, the lower tension spring 46 extends between a lower abutmentsurface 45 on the sliding valve 42 and an outward facing abutmentsurface 45′ in a recess by the upper end of connector 3.

In order to make the valve body 39 retain the ball 37 at an upper limitof travel, clear of the seating area 38, partly when the jar device isnot in the actuated state and partly during the relevant periods of thepercussion cycle, the valve body is provided with a valve spring 47. Thevalve spring 47 extends between a lower end face on the fins 41 of thevalve body 39 and an upper abutment surface 44 on the sliding valve 42.The valve body 39 further has at least one gateway 48 that enableshydraulic liquid to pass from the casing member bore 2 into a bore 49 inthe bottom end of the valve body 39 and then out of this, among otherthing to the bore 4 in the connector 3.

The special design of the piston valve 37, 38, 39 ensures that the valvedoes not inadvertently close off the passage of the piston bore 34before the impact area 21 of the impact collar 20 has reached fullimpact against the impact area 22 is of the end socket 8. Consequently,it will not be possible for hydraulic liquid to become trapped on theupper side of the piston 27, as such premature closing would have brakedthe piston 27 and given a reduced percussion effect during thepercussion cycle.

In the following, the principle of operation of the jar device will beexplained with reference to the drawings.

In a non-actuated state of the jar device, the impact area 21 of theimpact collar 20 is, as shown in FIG. 2, located in the immediatevicinity of the impact area 22 of the jar 7. The valve spring 47 and thevalve body 39 further lift the ball 37 off the seating area 38, to leavethe piston valve open. With this, hydraulic liquid has a clear passagevia the bores, the bore and gateway (19), respectively, of therespective components of the jar device. Furthermore, the jar device isheld in this non-actuated state and is also subjected to an upward forcefrom an pre-tensioned spring (not shown) positioned in a suitablelocation in the pipe string.

When increasing the flow of hydraulic liquid, the bottom valve body 39and thereby the ball 37 are displaced downward by the valve spring 47being compressed, as can be seen from FIG. 3. The ball 37 closes off thepassage of liquid through the piston 27 by sealing against the seatingarea 38. The hydrostatic pressure, which among other things acts on theupper surface 36 of the piston 27 and the ball 37, displaces the piston27 and the jar 7 to a lower limit of travel just before the percussionis triggered by the opening of the piston valve, see FIG. 4. At thislower limit of travel, the spring tension of the lower tension spring 46against the sliding valve 42 has reached a value exceeding the pressurefrom the inflowing hydraulic liquid against the ball 37. Consequently,the spring tension will, via the sliding valve 42 and the valve body 39,displace the ball 37 from the seating area 38 to re-open the valve, seeFIG. 5. Alternatively, the piston valve may open when the lower end ofthe sliding valve 42 abuts the upper end face of the connector 3. By thelatter alternative, a continued inflow of liquid will contribute to thevalve body 39 lifting the ball 37 off the seating area 38 in order toopen the valve.

The pressure drop that results from the opening of the piston valve (37,38, 39) allows liquid again to flow through the piston bore 34. Withthis, the spring tension from the tension spring 46 will displace thesliding valve 42 upwards while the valve body 39 displaces the ball 37off the seating area 38 and the piston 27 upwards in the casing member1, whereby the spring tension from the pre-tensioned spring (not shown)will be conductive to the impact area 21 of the impact collar 20 beingled to impact against the impact area 22 of the end socket 8 by theupper end of the casing member 1.

The piston 27 at the end of the jar 7 and the ball 37 in the piston bore34 must be provided with piston areas that can cause the piston valve tobe closed and opened in the manner intended. Likewise, the springtension in the valve and tension springs 46, 47 must be selectedaccording to the pressure conditions in the hydraulic liquid being fedto the jar device. In the embodiment shown, the closing and opening ofthe valve in the piston 27 is controlled by a valve ball 37 and a valvebody 39, i.e. two separate parts. These may however be made up from onesingle part, which will be a combined unit of these with an upperportion adapted to seal against the seating area 38 of the piston bore34.

The following describes, with reference to FIGS. 7 to 11, an embodimentin which the jar device is designed to strike downwards.

The present jar device for downward percussion comprises a tubularcasing member 1 with a longitudinal through bore 2 for allowinghydraulic liquid to pass through the casing member 1. The upper end ofthe casing member 1 is connected to a connector sleeve 3 in anappropriate manner, e.g. by means of a pressure tight threadedconnection 5 formed internally of the bore 2. The upper end of the jardevice may thereby in a suitable manner be coupled to a pipe string (notshown), e.g. by means of a pressure tight threaded connection 6 locatedinternally of an upper bore 16 in the upper connector sleeve 3. A lowerbore 4 extends further down through the connector sleeve 3 as acontinuation of the upper bore 16, to allow hydraulic liquid from thepipe string to pass through the upper connector sleeve 3.

The lower end of the casing member 1 is designed such that the casingmember 1 may be displaced externally along a jar 7. The jar 7 has anexternal impact area 109, preferably extending at right angles to thejar 7 around its entire periphery. Over the impact area 109, the jar 7has an upper section 110 extending upwards in the casing member bore 2.The external diameter of the upper jar section 110 is considerablysmaller than both the external diameter of the jar 7 under the impactarea 109 and the diameter of the casing member bore 2. The upper end ofthe jar section 110 is provided with a sleeve 111 fixed to the upper jarsection 110 e.g. by means of a threaded connection 112, so that the areaof an upper abutment surface 113 by the upper end of the upper jarsection 110 may be increased. The external diameter of the jar sleeve111 is a little smaller than the diameter of the casing member bore 2,to allow hydraulic liquid to flow past an end face 114 of the jar sleeve111. The jar 7 and the upper jar section 110 have a longitudinal throughbore 18 that allows hydraulic liquid to pass through the jar 7. Inaddition, the jar 7 is coupled to the relevant tool, pipe string etc. ina pressure tight manner by means of e.g. a lower, male threadedconnection 116.

In order to enable the casing member 1 to be displaced along the upperjar section 110, the lower end of the casing member 1 is provided withan end socket 117. The casing member 1 and the end socket 117 are fixedto each other, e.g. by means of a threaded, pressure tight connection118. Moreover, the end socket 117 is designed to abut the outerperiphery of the upper jar section 110 in a sliding manner when the jar7 is displaced along it during the percussion cycles. The end socket 117may be provided with internal, longitudinal grooves that arecomplementary to grooves in the outer periphery of the upper jar section110, whereby interrotation between the jar 7 and the end socket 117 isprevented. The end socket 117 is made pressure tight against the upperjar section 110 by means of e.g. an upper compression packing 119 and alower, relatively wide seal 120. Furthermore, the lower end of the endsocket 117 is provided with an impact area 121 that is located above theimpact area 109 of the jar 7, and which is designed to impact againstthe impact area 109 of the jar 7 during the percussion cycle of the jardevice.

Below a lower section 123 of the connector sleeve 3, the casing memberis equipped with a piston 27 that causes the casing member 1 to bemovable up along the upper section 110 of the jar in advance of eachsingle percussion of the jar device. The lower end of the connectorsection 123 is provided with a recess 124 having a fit such that anupper section of a longitudinal valve guide 34′ that, together with abore 34, constitutes a through bore in the piston 27, may locate in therecess 124, partly when the jar device is not actuated for percussivemotion and partly during periods of the percussion cycle, such as shownin FIGS. 7 a and 8 a. The lower end of the lower bore of the connectorsleeve 3 is fitted with an end piece 125 where hydraulic liquid may passfrom bore 4 to at least valve guide 34′ via a plurality of orifices 126running at an angle down through a transition zone between the wall ofthe recess 124 in the connector sleeve section 123 and the end piece125.

A midsection of the piston bore 34, 34′ is provided with a shoulder 130projecting into the piston bore 34, 34′. A valve ball 37 is placed inthe valve guide 34′ above the shoulder 130. The shoulder 130 has anupper seating area 38 that allows the ball 37 to seal against the pistonshoulder section 130 in advance of each percussion during the percussioncycle. The seating area 38 of the shoulder 130 and the ball 37 willthereby form a valve that may close and re-open, respectively, thepassage for the hydraulic liquid in the piston bore 34, 34′ during therespective periods of the percussion cycle. The ball 37 otherwise has adiameter essentially corresponding to the diameter of the valve guide34′, see FIG. 11 b, whereby is achieved accurate and safe control of theball 37 towards the seating area 38 during closing. The valve mechanism37, 34′, 38 is relatively insensitive to lateral accelerations.Hydraulic liquid may pass by the ball 37 via a plurality of passages 129running externally of the valve guide 34′ over the shoulder 130, partlywhen the jar device is not actuated for percussive motion and partlyduring periods of the percussion cycle, as shown in FIGS. 7 a and 10 a.As compared with other types of valve bodies, a ball 37 has a relativelysmall mass and thereby a low mass moment of inertia. A low mass momentof inertia will, together with the favourable fluid flow resistance of aball 37, cause the jar device to be able to work at a higher percussionfrequency than jar devices according to prior art.

The outside of the piston 27 is designed so as to allow it to slidinglyabut the inner wall of the casing member bore 2 during the percussioncycle, and the piston 27 is pressure tight against the casing memberbore 2 through a central compression packing 30 and relatively wide,upper and lower seals 31, 133, respectively. Moreover, the piston 27 isprovided with at least one upper bore 135 extending essentiallyvertically down from the upper end face of the piston and further intothe passage 129. This at least one bore 135 allows hydraulic liquid tobe controlled to an annulus 151 over the top surface 27′ of the piston27, and may allow hydraulic liquid that is undesirably located in thesame annulus 151, to escape via the bore 135 and further out through thepassages 129 in the piston 27.

The jar device also comprises a displacement piece 136 that extendsbetween the lower end of the piston 27 and the upper abutment surface113 of the jar section 110 with the associated jar sleeve 111. Thedisplacement piece 136 causes the casing member 1 to be movable up alongthe jar section 110 when the piston 27 is displaced downwards relativeto the casing member 1 in advance of the percussion of each percussioncycle. The displacement piece 136 has an external diameter that isconsiderably smaller than the diameter of the casing member bore 2, andalso a longitudinal through bore 137 for passage of hydraulic liquidthrough the displacement piece 136. The upper end of the displacementpiece 136 has been guided into an enlargement of the lower section ofthe piston bore 34. The lower end of the displacement piece 136 has anenlarged section 138 abutting the upper abutment surface 113 of theupper jar section 110 and the associated jar sleeve 111.

The upper section of the displacement piece 136 has a plurality oflongitudinal elongated slots 139 that allow hydraulic liquid to passfrom the bore 137 and out into the annulus 152 between the displacementpiece 136 and the casing member bore 2. Further, there is a valve body39 in the casing member bore 2, associated with the piston 27. An uppersection 141 of the valve body 39 has been carried upwards in the pistonbore 34. The external diameter of the upper valve body section 141 is alittle smaller than the opening through the shoulder 130 of the piston27, so as not to impede the passage of liquid. The upper end of thevalve body section 141 has a seating area that will normally abut theball 37. Likewise, the lower end of the end piece 125 has, at the outletof the connector bore 4, a corresponding seating area that may abut theupper side of the ball 37, as shown in FIGS. 7 a and 8 a.

A lower section 142 of the valve body 39 extends downwards in the upperend of the bore 137 of the displacement piece 136, and the externaldiameter of the lower valve body section 142 is formed so as to allowthe formation of a passage 143 for the hydraulic liquid between thelower valve body section 142 and the displacement piece 136. The lowervalve body section 142 is furthermore equipped with fins 144 carried outthrough the elongated slots 139 at the upper end of the displacementpiece 136. Side faces on the fins 144 of the valve body 39 slidinglyabut adjacent faces in the elongated slots 139 of the displacement piece136, and end faces 153 on the fins 144 slidingly abut the inside wall ofthe bore 2 of the casing member 1. Consequently, the valve body 39 maybe displaced relative to the displacement piece 136 during thepercussion cycle, as shown in FIGS. 8 a and 9 a. The fins 144 have anupper abutment surface 145 for the lower end face 154 of the piston 27,and a lower abutment surface 45 for a tension spring 46 associated withthe valve body 39.

The tension spring 46 enables the valve 39 in the piston 27 to be openedin order to trigger each percussion during the percussion cycle, i.e. bydisplacing the ball 37 up from the seating area 38 on the pistonshoulder 130. The tension spring 46 is positioned in the annulus betweenthe exterior face of the displacement piece 136 and the inside wall ofthe casing member bore 2. The tension spring 46 further extends betweenthe lower abutment surface 45 on the fins 144 of the valve body 39 andan upper abutment surface 149 on a shoulder 148 that projects into thecasing member bore 2 by an area near the place where the upper abutmentsurface 113 of the jar section 110 with the associated jar sleeve 111will be when the jar device is not actuated for percussive motion. Thebore through the shoulder 148 has a fit that allows hydraulic liquid toflow past it unimpeded in the casing member bore 2. The tension spring146 is otherwise designed in a manner such that the tension spring 46will only be compressed in order be tensioned by the valve body 39 whenthe ball 37 is placed sealingly in the shoulder 130 of the piston 27 andthe hydraulic pressure over the ball 37 in the jar device exceeds apredetermined value, while the tension spring 46 will only open thevalve in the piston 27 when the tension spring 46 has reached anotherpredetermined higher value that exceeds the hydraulic pressure appliedto the jar device.

Selecting an appropriate length for the displacement piece 136 andposition for the seating area 38 on the shoulder 130 for the ball 37, aswell as the distance between the lower abutment surface 45 on the fins144 of the valve body 39 and the seating area 38 for the ball 37, canensure that the valve 37, 38 in the valve guide 34′ does not in anundesirable manner close before the impact area 121 of the end socket117 has reached full impact against the impact area 109 of the jar 7.Thus it is made certain that hydraulic liquid located over the ball 37during this phase of the percussion cycle is not able to force the ballagainst the seating area 38 of the shoulder 130 so as to close the valveand trap hydraulic liquid. This avoids such potentially trapped liquidon the underside of the piston 27 braking the piston stroke and giving areduced percussion effect during the percussion cycle.

In the following, a brief explanation will be given of the principle ofoperation of the downward striking jar device, with reference to thedrawings.

In a non-actuated state of the jar device, the impact area 121 of theend socket 117 is, as shown in FIGS. 7 a and 7 b, located a smalldistance above the impact area 109 of the jar 7. Further, the valve body39 lifts the ball 37 off the seating area 38 of the shoulder 130, sothat the piston valve is open and the ball 37 abuts the seating area ofthe end piece 125 at the lower end of the connector 3. This leaves aclear passage for hydraulic liquid via the bores and passages of therespective components of the jar device. The jar device is maintained inthis non-actuated state by force from at least one pre-tensioned spring(not shown) or similar positioned at a suitable place in the pipestring.

The jar device is actuated by further compression of the tool, see FIG.8. The lower jar 7 moves the piston 27 upwards in the bore 2 relative tothe ball 37 via the displacement piece 136, so that the seating area 38of the piston seals against the ball 37. The ball 37 will in this phaseof the percussion cycle be held in place in the seating area 38 by theend piece 125 of the connector 3. At the same time, the hydrostaticpressure exerts a force against the ball 37 which forces it against theseating area 38 of the piston 27. During this phase of the percussioncycle, liquid flows through the relatively narrow bore 135 to the upperside of the piston 27. By the pressurised liquid filling the annulus 151relatively slowly, the acceleration of the piston 27 at the startingmoment is reduced, so that the ball 37 remains in sealing contact withthe seating area 38.

The hydrostatic pressure displaces the piston 27 and the ball 27downwards in the bore 2 of the casing 1, see FIG. 9, where the piston 27is at/near its lower limit of travel. At the same time, the valve body39 under the ball 37 is compressing the tension spring 46, and the jardevice is extended by the piston 27 moving the end socket and casingmember 1 upwards relative to the jar 7, via the displacement piece 136.This extension will, together with the increase in hydrostatic pressureupstream of the jar device, cause a tensioning of the spring packetabove (not shown).

During the further displacement of the piston 27 along with the valvebody 39 in the casing member bore 2, the hydrostatic pressure keeps thevalve closed until the tension spring 46 reaches a spring tension thatexceeds the hydrostatic pressure, as can be seen from FIGS. 9 a and 9 b.

When this spring tension is achieved, the tension spring 46 willdisplace the ball 37 off the seating area 38 on the valve shoulder 130,via the valve body 39, so that the piston valve is re-opened to triggerthe percussion, see FIG. 10. Alternatively, the valve body 39 will pushthe ball 37 off the seat 38 if the tension spring 46 reaches the bottom.

The pressure drop at the opening of the valve in the piston 27 meansthat the liquid may again flow through piston bore 34. At this, thespring tension in the tension spring 46 will displace the valve body 39and the piston 27 abutting the upper abutment surface 145 on the fins144 of the valve body 39, back into the casing member bore 2. At thesame time, the movement of the piston 27 causes the impact area 121 ofthe end socket 117 to impact on the impact area 109 of the jar 7 bymeans of the force from the pre-tensioned spring (not shown) in the pipestring.

The length of among other things the displacement piece 136 relative tothe seating area 38 for the ball 37 in the piston 27 will furthermorecause the valve in the piston 27 to remain open until the impact area121 of the end socket has impacted on the impact area 109 of the jar 7.The hydraulic liquid may if required have a possibility of passingthrough passage 135 at the upper end of the piston 27.

Those skilled in the art will appreciate that the piston 27 in thecasing member bore 2 and the ball 37 in the valve guide 34′ must beprovided with piston areas that cause the piston valve to be closed andopened in the manner intended. Likewise, the spring tension of thetension spring 46 must be selected on the basis of the pressureconditions in the hydraulic liquid flowing into the jar device. In theembodiment shown, a ball 37 and a valve body 39, i.e. two separateparts, control the closing and opening of the valve in the piston 27.These may however be made up of one single part, which will be acombined unit of these with an upper section adapted for sealing againstthe seating area 38 on the shoulder 130 in the piston bore 34.

During the percussion cycle, there will also be an approximatelyconstant flow of drill fluid through the jar device by the piston 27being displaced downwards, thus displacing fluid from the underside ofthe piston 27 during that part of the percussion cycle where the ball 37shuts off the flow in the piston 27.

1. A hydraulic jar device, for use in underground wells, where the jardevice is installed in a pipe string led down into the well, anddesigned to provide upward or downward percussions from the jar device,where the jar device comprises: a casing member, a connector sleeve, anda jar, the casing member and connector sleeve each having separatelongitudinal through bores, while the jar has a bore and a gateway sothat hydraulic liquid may pass in the jar device, and where the jardevice is provided with a piston associated with a valve, comprising: aball, a valve seat having a curved contact surface, and a lower valvebody, designed to close and open a bore during the percussion cycle, thepiston valve being designed, respectively, to close off the inflowinghydraulic liquid and to open when the spring force of a tension springexceeds the pressure from the inflowing hydraulic liquid, so that thepiston will displace the jar relative to the casing member, whereby thejar exerts a force against the casing member in order to carry out thepercussion, characterized in that a guide is positioned in the immediatevicinity of the valve seat and designed to prevent the ball frommovement in the lateral direction of the jar device or when the jardevice undergoes a strong lateral acceleration, the guide and the valveseat being made up of surface parts of the same piece of material. 2.The hydraulic jar device according to claim 1, characterized in that theball is adapted to seal against the valve seat.
 3. A method fordislodging a stuck object in a wellbore, comprising; positioning adownhole tool adjacent the stuck object, the downhole tool comprising: abody having at least one fluid pathway constructed and arranged to allowfluid to selectively flow therethrough; a valve body movable between afirst position and a second position relative to the body; a biasingmember biasing the valve body in the first position to allow fluid toflow through the at least one fluid pathway; and a movable piston havinga valve seat; a closure member for selective engagement with the valveseat, pumping fluid through the at least one fluid pathway; urging theclosure member into substantial contact with the valve seat and closingthe flow of fluid through the at least one fluid pathway; moving thepiston and valve body to the second position by fluid flow, therebycompressing the biasing member; separating the closure member from thevalve seat; and urging the valve body against the piston while returningthe valve body to the first position, thereby causing the piston toexert a force against the body for dislodging the stuck object.
 4. Themethod of claim 3, further including preventing lateral movement of theclosure member relative to the body.
 5. The method of claim 3, furthercomprising extending the biasing member, thereby returning the valvebody to the first position.
 6. The method of claim 3, wherein the jarmember is moved by the piston.
 7. The method of claim 3, wherein urgingthe closure member into substantial contact with the valve seatcomprises compressing a second spring.
 8. The method of claim 3, whereinthe force of the biasing member is greater than a hydraulic force actingon the piston.
 9. The method of clam 3, further comprising providing thejar member with an impact shoulder, the impact shoulder adapted toengage an impact area.
 10. The method of claim 9, wherein moving thepiston to the second position increases the distance between the impactshoulder and the impact area.
 11. The method of claim 10, whereinexerting the force for dislodging comprises engaging the impact shoulderwith the impact area.
 12. A hydraulic jar device for use in a well,comprising: a casing member having a longitudinal bore therethrough, apiston disposed within the casing member and adapted to apply a forceagainst the casing member, the piston having a fluid bore; a valve bodyfor selective engagement with the piston; a biasing member adapted tomove the valve body between a first position and a second position,wherein in the first position, the valve body is urged against thepiston and the fluid bore is open, and in the second position, thebiasing member is compressed and the fluid bore is closed.
 13. The jarof claim 12, wherein the force is applied against the casing member whenthe valve body moves from the second position to the first position.